The present invention relates generally to the field of induction hardening and the apparata and equipment normally associated with induction hardening machines. More specifically the present invention relates to the design of centering spindles which are used as part of induction hardening machines in order to support a workpiece, such as vertical centers (spindles) supporting a shaft.
Spindles of the type which have generally been described frequently include a bearing arrangement of some type which may include ball bearings, needle bearings, or both. What has been discovered is that the electromagnetic fields that are typically produced by induction hardening machines are transmitted to or through these bearings. These field currents tend to arc through the bearings and the lubricating medium and cause early failure through pitting and other conditions which are detrimental to bearing life.
Another aspect of using centering spindles which directly contact the workpiece is that the heat from the workpiece is transferred through the spindle to the bearings. Due to the substantial heat which is generated in the workpiece as part of the induction hardening process, heat transfer to the bearings can contribute to early or premature bearing failure.
A further consideration in the design of centering spindles of the type described herein is the mechanical wear on that portion of the centering spindle which directly contacts the workpiece. While there is some wear due to axial loading, it is the combination of rotary motion and axial loading which causes, over time, wear to occur. Wear to the tip of the centering spindle can affect the preciseness of the rotary motion which is to be imparted to the workpiece. Wear to the end or tip of the centering spindle can also affect the ability of the centering spindle to properly support the workpiece and maintain the necessary orientation for the workpiece. Wear to the end or tip of the centering spindle will ultimately force the centering spindle to be replaced.
It would be an improvement to the design of centering spindles of the type described herein which are used with induction hardening machines to electrically isolate or insulate the bearings from the current of any electromagnetic field which may be created during the induction hardening process. A further improvement would be to thermally isolate or insulate the bearings from the heat generated in the workpiece. A still further improvement would be to redesign the centering spindle so that only the worn tip or end portion of the centering spindle would actually have to be replaced, instead of the current practice of replacing the entire spindle when the degree of wear on the tip becomes unacceptable.
The present invention provides each of these improvements in a novel and unobvious manner as described and claimed herein.